The therapeutic improved event-free survival and 95% of participants were alive and event-free as of 27 September 2018.

SMA is a severe neuromuscular disease that leads to progressive muscle weakness and paralysis. The genetic condition is a leading cause of infant mortality.

If left untreated, 50% of babies with SMA Type 1 would not survive or need permanent ventilation by the age of 10.5 months.

Zolgensma is designed to target the monogenic root cause of the disease and prevent further muscle deterioration by providing a functional copy of the human SMN gene using adeno-associated viral vector 9 (AAV9).

“These STR1VE data reinforce what was seen in the pivotal Phase I START trial, including trends toward prolonged survival and milestone achievement.”

The open-label, single-arm, single-dose, multi-centre STR1VE trial was conducted to assess the safety and efficacy of a one-time intravenous infusion of the gene therapy in patients aged less than six months.

According to the interim data, the median age during the study was 9.5 months, and 86% of the patients who could reach 10.5 months of age were event-free.

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Zolgensma also demonstrated an increase in the Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND) scores, which represents an improvement in motor function from baseline.

Subjects in the gene therapy arm were also found to achieve motor milestones, with an increase in the number of patients who were able to sit without support for a minimum of 30 seconds.

Further analysis found the safety profile of Zolgensma similar to that observed in the previous Phase I START trial. The STR1VE study is expected to be completed next year.

AveXis chief medical officer Olga Santiago said: “These STR1VE data reinforce what was seen in the pivotal Phase I START trial, including trends toward prolonged survival and milestone achievement never seen in the natural history of the untreated disease.

“With a patient population and baseline characteristics closely matched to the START trial, these data build upon the body of evidence supporting the use of Zolgensma for SMA Type 1.”